Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

688
FXUS63 KLOT 240521
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1121 PM CST Fri Jan 23 2026

.KEY MESSAGES...

- Bitterly cold conditions will persist through early Saturday
  morning.

- Fluffy accumulating snow paired with cold temperatures will
  likely lead to hazardous travel conditions in some locations
  late Saturday into Sunday. The greatest likelihood for this is
  currently forecasted to be near and east of Interstate 55.

- Lingering lake effect snow for far northeastern IL and
  northwest IN Sunday night through Monday morning. Some
  additional accumulation is likely.

&&

.UPDATE...
Issued at 859 PM CST Fri Jan 23 2026

The main concern in the near term is focused primarily on the
persistent lake effect snow ongoing across northern portions of
Porter county IN. The Arctic airmass over the "relatively warm"
lake water continues to be effective at generating shallow, but
somewhat intense convective snow showers across the
southern/southeastern shore of Lake Michigan this evening. Over
the past few hours web and plow cams across northern Porter
county have shown snow covered roads, along with locally reduced
VSBYs (~1 mile or less). Expect these snow showers (and the
associated slick travel conditions) to continue here through the
evening, before veering flow over the south end of the lake
begins to dive the lake effect snow offshore overnight. The most
impacted areas from this snow are expected to remain generally
along and north of U.S. 30 in Porter county. Given the ongoing
slick travel conditions, we did consider a short fussed Winter
Weather Advisory, but instead opted to reissue the SPS and GNOW
graphic through late this evening.

Outside of the lake effect, the ongoing Cold Weather Advisory
will continue through 9 AM Saturday morning. No changes are
planned to this as wind chills across the area continue to
hover in the -20 to -29 range in most areas.

The forecast for late Saturday into Sunday remains unchanged at
this time. The incoming 00Z guidance continues to support snow
development either late Saturday afternoon (after 3-4 pm) or
Saturday evening. Once it onsets, the very cold conditions will
allow roads to quickly become snow covered and slick Saturday
evening. As mentioned in the previous discussion below, a Winter
Weather Advisory is likely (70%+)to be needed for at least
southern/southeastern sections of the area, and possibly for
areas along the Lake Michigan lakeshore as well due to lake
enhanced snow late Saturday night into Sunday.

KJB

&&

.DISCUSSION...
Issued at 244 PM CST Fri Jan 23 2026

Through Sunday:

Main focus is on a synoptic accumulating snow system Saturday
afternoon through Sunday. Some questions remain with exact snow
amounts especially into the Chicago metro area where some lake-
enhancement is likely. Expectation is that we`ll end up with a
general 3-6" accumulation across the southeast third to half of
the cwa, and potentially parts of the Chicago metro where lake-
enhancement occurs, with a sharp gradient to lower amounts
farther to the northwest. Details of where exactly this gradient
lays out will need further refinement, and thus in
collaboration with neighbors to the east and west have held off
on headline issuance just yet. However, we do anticipate the
need for a winter weather advisory for southeast parts of the
forecast area and near the lake as the footprint is further
narrowed down.

In the near term, very cold arctic air remains in place across
the area this afternoon, with temperatures still in the negative
single digits across most of the area as of 2 pm CST. Winds
have eased since this morning, allowing wind chills to settle
around -25F or so north of I-80, and had allowed the Extreme
Cold Warning to expire at noon as scheduled. Even with lighter
winds however, overnight temps of -5F to -15F will support wind
chills of -20F to -29F into Saturday morning, and a Cold Weather
Advisory remains in effect for the entire area through 9 am CST
Saturday.

Additionally, light but persistent lake-effect snow
showers persist across parts of northwest Indiana, particularly
northeast Porter County. Relatively shallow-topped, disorganized
multi-band setup is not expected to produce impressive snowfall
rates, though cold temperatures are allowing the persistent
light snow to accumulate on roadways resulting in slippery
travel conditions. With limited area have continued Special
Weather Advisory issuance for these conditions which will likely
persist into this evening. Forecast soundings overnight then
depict lowering inversion heights, decreasing winds/increasing
shear along with a gradual development of a land-breeze
convergent zone which shifts westward toward Lake County IN with
time before eventually focusing further out away from the lake
shore by morning. While this scenario appears reasonable, we`ll
have to continue to monitor light LES trends through the night.

Attention then turns to the more widespread accumulating snow
system expected to affect the area later Saturday afternoon
through Sunday. Evolution of this system remains somewhat
complex, involving the upper low currently off the Baja coast
being kicked eastward by another wave dropping southeast across
CA/NV. This results in a broad area of warm advection/isentropic
ascent developing along the established baroclinic zone from
the Southern Plains to the Ohio Valley Saturday and a broad
synoptic precipitation shield of which the northern periphery
remains progged to extend into northern IL/IN. While the
strongest forcing and axis of heaviest precipitation is expected
to remain south of the region, models continue to depict
deepening saturation within a thermal profile which features a
deep DGZ across the area from Saturday afternoon into Sunday.
Ensemble probabilities of 6" or more of snowfall remain across
central IL/IN for the most part, guidance is in pretty good
agreement with amounts in the 3-6" range across our southeastern
cwa.

Furthermore, a deepening layer of northeasterly low-level flow
is likely to producing some degree of lake- enhancement into
parts of the Chicago metro area, possibly with an additional
small footprint of 3-5" amounts there (perhaps locally 5-6").
Will likely need a Winter Weather Advisory for at least the
southeast part of the cwa from Saturday afternoon into Sunday,
though with some of these details still uncertain and in
collaboration with neighbors to my east and west have held off
issuance at this time. Amounts should diminish quickly farther
to the northwest. Synoptic snow looks to taper off/end from the
west/northwest Sunday afternoon, though with some lingering
lake effect lingering into Sunday night.

Ratzer


Sunday Night through Friday:

The main snow shield will be in the process of exiting the area
from west to east Sunday afternoon and evening as the surface
low over the Tennessee and Ohio River Valleys pushes into the
Mid-Atlantic. While this will bring the snow to a close for
most, a band of lake effect snow is expected to be ongoing as a
couple of vort lobes within the upper trough pivot through. Now
where exactly this lake effect band will be Sunday evening
remains a bit uncertain, but as winds turn more northwesterly
late Sunday evening and overnight the band should pivot into
northwest IN and eventually into northern IN by midday Monday.

Regardless of the band`s location, forecast soundings do show
much of the atmosphere in the snow growth region with steep low-
level lapse rates (7-8C/km) and 5000-6000 ft lake induced ELs.
These parameters should be sufficient to support snowfall rates
around 0.5 to 1.0" per hour which will result in at least a
couple inches of additional accumulation Sunday night through
Monday morning. Given that surface temperatures will still be in
the 5-10F range, road treatments will likely struggle to combat
the snow and lead to hazardous travel beneath the lake effect
band. So despite the uncertainty in location those near the lake
from Chicago, IL to Michigan City, IN should be prepare for
travel impacts Sunday night into Monday morning.

Outside of the lake effect, the main forecast concern for the
rest of the week will be the continued below average
temperatures. The reason for the continued cold will be the
upper troughing that is forecast to establish over the Great
Lakes this weekend and persist through at least the end of next
week. As a result, northwest winds will prevail and continue to
pump colder arctic air into the region keeping afternoon highs
in the teens to around 20 with overnight lows in the single
digits (possibly below zero at times). From a precipitation
perspective, the troughing overhead will allow several
shortwaves to dive across the region throughout the week and
some of them could bring periods of snow. At this point, it
seems guidance is favoring a period towards the later half of
the week for one of these disturbances to move through but
confidence remains low on its exact track and what if any
impacts it will bring locally. So be prepared for additional
periods of snow at times and stay tuned for more details as we
get closer.

Yack

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1121 PM CST Fri Jan 23 2026

Main Concern:

- Accumulating light snow overspreading the area late day
  Saturday into Saturday evening, especially for the Chicago
  metro, but may include RFD area as well.

Primarily VFR conditions (except MVFR CIGs initially at GYY)
with much lighter winds are in store through much of Saturday.
This will be followed by developing light snow and associated
lower flight categories towards and especially after sunset on
Saturday. The main item of lower confidence in the snow forecast
is onset time due to uncertainty regarding the erosion of dry
air before snow reaches the surface. With this being said, more
recent forecast soundings suggest that at least persistent
flurries may be able to break through the dry air sooner. If
this occurs, IFR VSBY snowfall may also develop sooner. In the
latest TAF, maintained PROB30 mention at all the Chicago metro
TAF sites from the late afternoon into early evening, but with
2SM VSBY to account for the aforementioned earlier onset.

Confidence is still higher in prevailing IFR VSBY light snow
(~1-2SM) starting by around 02z Saturday evening. CIGs or VV
should be in the 1500-3000 ft range. Expect wind direction
variability right over Chicago (northerly at ORD and easterly at
MDW) during this time as well. Forecast accumulations are up to
1-2" of fluffy snow by early Sunday. With recent trends towards
the dry air being eroded enough for snow to develop at RFD,
opted for a PROB30 for 2SM VSBY snow there by late Saturday
evening.

Finally, at GYY, lake effect snow showers may push westward and
get close enough to result in on and off 4-6SM light snow late
tonight into Saturday morning (09-15z Saturday PROB30 in TAF).

Castro

&&

.HYDROLOGY...
Issued at 230 PM CST Fri Jan 23 2026

River gauges, reports from local officials, and reports from
trained ice spotters continue to indicate a few ice jams across
the area due to the significant increase in river ice over
recent days. With continued cold weather into next week,
conditions will remain favorable for river ice formation. While
no widespread flooding is expected, localized ice jams may
occur.

- NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Cold Weather Advisory until 9 AM CST Saturday for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-
     ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Cold Weather Advisory until 9 AM CST /10 AM EST/ Saturday for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 3 AM CST Saturday for Gary to Burns
     Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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